/Engine/Source/Editor/LevelEditor/Public/LevelViewportLayout.h
Checks to see the specified level viewport is visible in this layout A viewport is visible in a layout if the layout is visible and the viewport is the maximized viewport or there is no maximized viewport
true if the viewport is visible.
bool IsLevelViewportVisible ( [FName](API\Runtime\Core\UObject\FName) InViewport ) const